Relatively large phased array antenna architectures, such as but not limited to spaceborne, chirped synthetic aperture radar systems, typically contain a multiplicity of transmitters and receivers distributed across respective spaced apart arrays. In such a system, a common reference frequency is customarily supplied to all transmit and receive element groups of the array. As such, there is the issue of how to take into account phase shift associated with variations in the substantial length of signal transport cable that links a reference frequency source, used at one transmit/receive location in the array, with the a remote transmit/receive portion of the array.
Because terrestrial open loop calibration of the system suffers from the inability to take into account variation in temperature along the transport cable due to changes in sun angle, and variations in obscuration by components of the antenna support platform in the antenna's space-deployed condition, it has been proposed to perform temperature measurements at a number of locations along the cable and provide phase compensation based upon the measured values. A drawback of this approach stems from the fact that there are non-linearities within the cable, so that over different temperatures it is necessary to employ a larger number of values in the calibration table. In addition, because this scheme employs multiple measurement points along the cable, there are associated variations in loading which, in turn, introduce separate amounts of phase shift to the reference frequency signal.